Voltage-based auto-correction of switching time

ABSTRACT

A method for controlling a load-current zero-crossing of a switching regulator having a high-side switch and a low-side switch includes detecting, by a spike detection circuit, a presence of a spike on an output voltage of the switching regulator, determining, by the spike detection circuit, in the event that a spike is present, whether the spike is a positive spike or a negative spike, and adjusting a turn-off timing of the low-side switch based on a determination result.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/957,900, filed on Apr. 19, 2018, entitled “VOLTAGE-BASEDAUTO-CORRECTION OF SWITCHING TIME,” which is incorporated by referenceherein in its entirety.

FIELD OF THE INVENTION

The present invention relates generally to switching regulators. Moreparticularly, embodiments of the present invention relate to controlcircuits, devices, and methods of detecting and eliminating the presenceof spikes at a switching node of the switching regulators and optimizinga dead time in a switching module of the switching regulators.

BACKGROUND OF THE INVENTION

Voltage regulators have been employed for providing stable supplyvoltages to a large variety of electronic products. FIG. 1 schematicallyshows a switching voltage regulator 100, which includes a high-sideswitch 102 and a low-side switch 104 connected between an input voltageVin and ground GND to be alternatively switched by a controller 106, acurrent sense circuit 108 senses an output current Iout flowing throughan inductor L to charge a capacitor C to produce an output voltage Vout.Current sense circuit 108 senses the output current Iout to provide acurrent Isense to controller 106, which then turns on and off high-sideswitch 102 and low-side switch 104 to maintain a desired voltage levelof the output voltage Vout.

However, improper turn-on and/or turn-off times of high-side switch 102and low-side switch 104 may cause a large shoot-current flowing throughthe switches when the turn-on time of both switches overlaps, orovershoot current/voltage and undershoot current/voltage when the idealswitching time of both switches is not well controlled.

Thus, there is a need for solutions to overcome the above-describeddrawbacks.

BRIEF SUMMARY OF THE INVENTION

Embodiments of the present invention provides circuits, devices, andmethods for correcting systematic offset or delay of a low-side switchin a switching voltage regulator. The offset or delay may cause glitchesat the switching node of the switching voltage regulator. The glitchesmay cause additional power loss to the switching voltage regulator andreduce its life expectancy.

In accordance with some embodiments of the present invention, a controldevice for a switching voltage regulator having a high-side switch and alow-side switch to supply a switching voltage to a load may include acomparator configured to compare the switching voltage with a referencevoltage to provide a disable (turn-off) signal to the low-side switch,and a spike detection circuit configured to receive the switchingvoltage and output an offset control signal to execute a time shift tothe disable signal.

In one embodiment, the spike detection circuit includes a first inputcoupled to the switching voltage, a second input coupled to a thresholdvoltage, and an output for providing the offset control signal to thecomparator.

In one embodiment, the comparator is a differential operationalamplifier having a first input coupled to the switching voltage, asecond input coupled to the reference voltage, and an output forproviding the disable (turn-off) signal to the low-side switch. In oneembodiment, the differential operational amplifier includes a variableresistive element.

In one embodiment, the spike detection circuit includes a firstdifferential operational amplifier for detecting a positive glitchassociated with a late off time of the disable signal, a seconddifferential operational amplifier for detecting a negative glitchassociated with an early off time of the disable signal, and a logiccircuit coupled to the first and second differential operationalamplifiers and configured to provide an indication signal indicating thepresence of a glitch and whether the glitch is a positive glitch or anegative glitch. In one embodiment, the spike detection circuit furtherincludes a digital-to-analog converter configured to convert theindication signal to an analog delay through adjusting a resistancevalue of the variable resistive element array.

In one embodiment, the high-side switch is a p-channel transistor, andthe low-side switch is an n-channel transistor.

Embodiments of the present invention also provide a switching regulatorincluding a controller for providing a first driver signal and a seconddriver signal, a dead-time control circuit having a first input terminalconnected to the first driver signal, a second input terminal connectedto the second driver signal, a first output terminal, and a secondoutput terminal, a switching module coupled to the first and second outterminals and configured to supply a switching voltage to an LC network;and a spike detection circuit configured to receive the switchingvoltage and provide a control signal to the dead-time control circuit.

In one embodiment, the dead-time control circuit may comprise twocross-coupled logic gates including a first logic gate having a firstinput connected to the first input terminal, a second input, and a firstoutput, a second logic gate having a third input connected to the secondinput terminal, a fourth input, and a second output; a first delayelement having a fifth input connected to the second output of thesecond logic gate and a third output connected to the second input ofthe first logic gate; and a second delay element having a sixth inputconnected to the first output of the first logic gate and a fourthoutput connected to the second input of the second logic gate. In oneembodiment, the first and second logic gates are not a same type logicgate.

In one embodiment, the first delay element and the second delay elementeach comprise RC elements. The RC elements may include a variableresistive element. In one embodiment, the variable resistive elementincludes a metal oxide semiconductor (MOS) transistor or a field effecttransistor.

In one embodiment, the switching module includes a p-channel transistorand an n-channel transistor connected in series between an input voltagesignal and ground.

In one embodiment, the spike detection circuit includes a differentialoperational amplifier having a first input for receiving the switchingvoltage, a second input for receiving a reference voltage, andconfigured to provide the control signal in response to a differencebetween the switching voltage and the reference voltage.

In one embodiment, the spike detection circuit further includes ananalog-to-digital converter configured to convert the control signal toan analog delay through for adjusting a resistance value of the variableresistive element array.

Embodiments further provide a method for controlling a turn-off time ofa low-side switch in a switching voltage regulator having a high-sideswitch and the low-side switch connected in series between an inputvoltage supply and ground. The method may include providing a spikedetection circuit coupled to the switching voltage regulator. The methodalso includes determining a glitch at a switching node of the switchingvoltage regulator. In one embodiment, the glitch may be a positiveglitch caused by a late turn-off of the low-side switch. In anotherembodiment, the glitch may be a negative glitch caused by an earlyturn-off of the low-side switch. In yet another embodiment, the glitchmay not be present when the low-side switch is turned at the correctinstant.

In one embodiment, the method may further include varying a slew rate ofan output signal of a comparator in response to the glitch. In oneembodiment, after determining that a glitch is present, the method mayalso provide a control signal to the comparator to vary the slew rate ofthe output signal according to the determined glitch. In one embodiment,the method may also include buffering the output signal, and providingthe buffered output signal to turn off the low-side switch.

Embodiments of the present invention also provide a method forcontrolling a dead time of a switching regulator comprising a switchingmodule and a controller providing first and second driver signals to theswitching module. The method may include providing a dead-time controlcircuit between the controller and the switching module and a spikedetection circuit between the switching module and the dead-time controlcircuit; monitoring a switching voltage at a switching node of theswitching module by the spike detection circuit; and determining whetherthe switching voltage exceeds a threshold voltage. In one embodiment, ifthe method determines that the switching voltage exceeds the thresholdvoltage, the method includes generating a control signal to thedead-time control circuit to adjust a dead time between the first driversignal and the second driver signal; and if the method determines thatthe switching voltage does not exceed the threshold voltage, the methodincludes maintaining the dead time between the first driver signal andthe second driver signal.

In one embodiment, the dead-time control circuit may include twocross-coupled logic gates including a first logic gate having a firstinput for receiving the first driver signal, a second input, and a firstoutput, a second logic gate having a third input for receiving thesecond driver signal, a fourth input, and a second output, a first delayelement having a fifth input connected to the second output of thesecond logic gate and a third output connected to the second input ofthe first logic gate, and a second delay element having a sixth inputconnected to the first output of the first logic gate and a fourthoutput connected to the second input of the second logic gate.

In one embodiment, determining whether the switching voltage exceeds athreshold voltage includes comparing the switching voltage with athreshold voltage to obtain the control signal, and converting thecontrol signal to an analog signal for adjusting the dead time.

In one embodiment, the method further includes iteratively monitoringthe switching voltage, comparing the switching voltage with thethreshold voltage, and adjusting the dead time until the switchingvoltage is lower than first threshold voltage.

The following detailed description together with the accompanyingdrawings will provide a better understanding of the nature andadvantages of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, referred to herein and constituting a parthereof, illustrate embodiments of the disclosure. The drawings togetherwith the description serve to explain the principles of the invention.

FIG. 1 is a schematic diagram of a conventional switching voltageregulator, as known in the art.

FIG. 2A is a graph illustrating the switching voltage LX and the outputcurrent Iout of the voltage regulator in FIG. 1 for the case where theturn-off time of the low-side switch is at ideal timing.

FIG. 2B is a graph illustrating the switching voltage LX, the outputcurrent Iout of the voltage regulator in FIG. 1 for the case where thelow-side switch is turned off late.

FIG. 2C is a graph illustrating the switching voltage LX and the outputcurrent Iout of the voltage regulator in FIG. 1 for the case where thelow-side switch is turned off early.

FIG. 3A is a simplified block diagram of a switching regulator accordingto an exemplary embodiment of the present invention.

FIG. 3B is a circuit diagram of a switching voltage regulator accordingto another exemplary embodiment of the present invention.

FIG. 4 is a circuit diagram illustrating a spike detection circuitaccording to an embodiment of the present invention.

FIG. 5A is a graph illustrating the turn-off signal for the low-sideswitch in response to an offset control signal according to anembodiment of the present invention.

FIG. 5B is a graph illustrating adjusted slew rates shown in FIG. 5Abeing converted to a digital turn-off signal for the low-side switchafter the output signal with adjusted slew rates passes through aninverter buffer according to an embodiment of the present invention.

FIG. 6 is a simplified flow chart of a method for controlling a turn-offtime of a low-side switch in a switching voltage regulator according toan embodiment of the present invention.

FIG. 7 is a simplified block diagram of a switching voltage regulatorfor minimizing power loss during a dead time according to an embodimentof the present invention.

FIG. 8 is a simplified circuit diagram of a switching voltage regulatorfor minimizing a dead time according an embodiment of the presentinvention.

FIG. 9 is a schematic circuit diagram of an RC delay element accordingto an embodiment of the present invention.

FIG. 10 is a graph illustrating waveforms of driver signals for therespective high-side switch and the low-side switch according to anembodiment of the present invention.

FIG. 11 is a simplified flow chart of a method for controlling a deadtime of a switching voltage regulator according to an embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

In the following description, numerous specific details are provided fora thorough understanding of the present invention. However, it should beappreciated by those of skill in the art that the present invention maybe realized without one or more of these details. In other examples,features and techniques known in the art will not be described forpurposes of brevity.

It will be understood that the drawings are not drawn to scale, andsimilar reference numbers are used for representing similar elements.Embodiments of the invention are described herein with reference tofunctional block diagrams that are schematic illustrations of idealizedembodiments (and intermediate structures) of the invention.

It will be understood that, when an element or component is referred toas “connected to” or “coupled to” another element or component, it canbe connected or coupled to the other element or component, orintervening elements or components may also be present. In contrast,when an element or component is referred to as being “directly connectedto,” or “directly coupled to” another element or component, there are nointervening elements or components present between them. It will beunderstood that, although the terms “first,” “second,” “third,” etc. maybe used herein to describe various elements, components, these elements,components, regions, should not be limited by these terms. These termsare only used to distinguish one element, component, from anotherelement, component. Thus, a first element, component, discussed belowcould be termed a second element, component, without departing from theteachings of the present invention. As used herein, the terms “logiclow,” “low state,” “low level,” “logic low level,” “low,” or “0” areused interchangeably. The terms “logic high,” “high state,” “highlevel,” “logic high level,” “high,” or “1” are used interchangeably.

As used herein, the terms “a”, “an” and “the” may include singular andplural references. It will be further understood that the terms“comprising”, “including”, having” and variants thereof, when used inthis specification, specify the presence of stated features, steps,operations, elements, and/or components, but do not preclude thepresence or addition of one or more other features, steps, operations,elements, components, and/or groups thereof. In contrast, the term“consisting of” when used in this specification, specifies the statedfeatures, steps, operations, elements, and/or components, and precludesadditional features, steps, operations, elements and/or components.Furthermore, as used herein, the words “and/or” may refer to andencompass any possible combinations of one or more of the associatedlisted items. The terms “Vsw” and “LX” are used interchangeably herein.

Referring back to FIG. 1, controller 106 receives feedback signalcarrying Isense information to control the turn-on and turn-off times ofhigh-side and low-side switches 102, 104 through respective gate driversignal Pgate 112 and Ngate 114. When Pgate signal 112 transitions from ahigh state to a low state (e.g., from Vin to 0V), high-side switch 102is turned on, and when Pgate signal 112 transitions to a high state,high-side switch 102 is turned off. Conversely, when Ngate signal 114transitions from a low state to a high state (e.g., from 0V to Vin),low-side switch 104 is turned on, and when Pgate signal 112 transitionsto a low state, low-side switch 104 is turned off. High-side andlow-side switches 102, 104 are alternatively turned on, so that they arenot turned on at the same time to avoid a shoot-through current. Theturning on of high-side switch sends a current Iout through the inductorL to charge the capacitor C to provide the output voltage Vout to aload.

FIG. 2A is a graph illustrating the switching voltage LX and the outputcurrent Iout for the case where the low-side switch is turned off at theideal time. Referring to FIG. 2A, at time <t0, both the high-side switchand the low-side switch are turned off. When controller 106 turns onhigh-side switch 102 at time t0, the input voltage Vin is supplied tothe inductor L at node LX 124, the current Iout rises with a constantslope 201 and starts charging the capacitor C. At time t1, controller106 turns off high-side switch 102 and turns on low-side switch 104, thecurrent Iout begins to fall with a constant slope 202. At t2, when Ioutcrosses the zero threshold, controller 106 turns off low-side switch104. The capacitor C smooths out the triangular current Iout to delivera DC current to the load.

FIG. 2B is a graph illustrating the switching voltage LX and the outputcurrent Iout for the case where the low-side switch is turned off late.Referring to FIG. 2B, instead of turning off low-side switch 104 at t2,controller 106 turns off low-side switch 104 late, the current Iout willundershoot the zero crossing before low-side switch 104 is turned off(at time t3). Then, the inductor L operates as a current source thatcontinues to deliver the undershoot current value and cause the voltageLX to rise from 0V to a peak voltage Vpeak Vd102 that is above Vin by anamount equivalent to the voltage drop across the body diode D102 (e.g.,0.7V). The negative current 213 will continue to flow through the bodydiode D102, and peak voltage Vpeak Vd102 will remain until the negativecurrent 223 decreases back to zero at t4. At this time, the switchingvoltage LX at node 124 is back to the desired output voltage Vout.

FIG. 2C is a graph illustrating the switching voltage LX, the outputvoltage Vout, and the output current Iout for the case where thelow-side switch is turned off early. Referring to FIG. 2C, instead ofturning off low-side switch 104 when Iout crosses the zero crossing,controller 106 turns off low-side switch 104 early, the current Iout isstill positive at t2. Both the high-side and low-side switches are nowturned off, the inductor will keep the current Iout to continue to flowthrough the body diode D104 of the low-side switch into the inductor, sothat the switching voltage LX is below ground (indicated by Vd104) whilethe positive current decreases to zero. The current flowing through bodydiodes D102 (FIG. 2B) and body diode D104 causes additional powerconsumption and heat dissipation in the switching regulator. Besides,the overshoot and undershoot values, Vd102 and Vd104, can causereliability issues for the pass devices 102 and 104. Accordingly, thepresent inventors provide novel technical solutions to avoid thesedrawbacks.

FIG. 3A is a simplified block diagram of a switching regulator 30A thatcan correct systematic offsets causing an early or late switching of thelow-side switch according to an embodiment of the present invention.Switching regulator 30A includes a switching voltage regulator 31, azero-cross comparator 33, a spike detection circuit 35. Switchingvoltage regulator 31 may include a first output terminal 311 forproviding a desired output voltage Vout to a load, a second outputterminal 312 for providing a switching voltage Vsw, and a first inputterminal 313. Zero-cross comparator 33 may include a second inputterminal 331 for receiving the switching voltage Vsw, a third inputterminal 332 for receiving a reference voltage Vref, a fourth inputterminal 333, and a third output terminal 334 for providing a turn-offsignal (disable) 343 to switching voltage regulator 31 through firstinput terminal 313. Spike detection circuit 35 may include a fifth inputterminal 351 for receiving the switching voltage Vsw, a sixth inputterminal 352 for receiving a threshold voltage Vthreshold, and a fourthoutput terminal 353 for providing an offset control signal 361 tozero-cross comparator 303. The terms “turn-off signal” and “disablesignal” are used interchangeably herein.

FIG. 3B is a circuit diagram of a switching regulator 30B according toan exemplary embodiment of the present invention. Referring to FIG. 3B,switching regulator 30B includes a switching voltage regulator 31Ahaving logic circuit 305 for driving a switching module including ahigh-side switch 302 and a low-side switch 304, a zero-cross comparator33A, and a spike detection circuit 35A. In some embodiments, high-sideswitch 302 may be a P-channel transistor, low-side switch may be anN-channel transistor. High-side switch 302 is turned on by a Pgatesignal at a low state (e.g., 0V) and turned off by the Pgate signal at ahigh state (e.g., Vin). When high-side switch 302 is turned on, thevoltage Vsw at node 324 will have substantially the voltage Vin.Low-side switch 302 is turned on by an Ngate signal at the high state(e.g., Vin) and turned off by the Ngate signal at the low state (e.g.,0V). When low-side switch 304 is turned on, the voltage Vsw at node 324will have substantially the voltage GND.

Referring back to FIG. 2A, the current Iout flowing through the inductorL increases linearly from OA to a certain value when high-side switch302 is turned on and low-side switch 304 is turned off (e.g., betweenthe time period t0-t1). The current Iout decreases linearly from thecertain value to OA when high-side switch 302 is turned off and low-sideswitch 304 is turned on (e.g., time period t1-t2). The capacitor C ischarged by the current Iout to provide a desired output voltage Vout.The turn-on and turn-off times of high-side and low-side switches arecontrolled by logic circuit 305 of the switching voltage regulator.There is no undershoot or overshoot in the switching voltage Vsw at node324 if logic circuit 305 turns off low-side switch 304 at the ideal timewhen the current Iout crosses zero (e.g., at time t2).

Referring back to FIG. 2B, in the case where logic circuit 305 turns offlow-side switch 304 late, the current Iout will overshoot the zerocrossing before low-side switch is turned off. The negative current willflow to ground through low-side switch 304. When low-side switch 304 iseventually turned off at time t3, the switching voltage Vsw at node 324will rises from 0V to above the supply voltage Vin by an amountequivalent to the body diode D302. The current continues to flow acrossthe body diode D302 of high-side switch 302, the switching voltage Vswremains at its peak value Vpeak until the current Iout decreases to OAat time t4. After that, the switching voltage Vsw returns back to thedesired output voltage value Vout.

Referring back to FIG. 2C, in the case where logic circuit 305 turns offlow-side switch 304 early, i.e., the current Iout has not reached thezero crossing at time t2, the inductor L will maintain the continuouscurrent flow so that the current Iout will flow across the body diodeD304 of low-side switch 304. The switching voltage Vsw will remain belowthe ground level (denoted by Vnegative) while the current Tout decreasesto OA at time t3.

The voltage overshoot and undershoot can be detected by spike detectioncircuit 35A. In one example embodiment, spike detection circuit 35Aincludes a differential operational amplifier 350 having a first input351 for receiving the switching voltage, a second input 352 forreceiving a first threshold voltage Vthreshold1, and a third input forreceiving a second threshold voltage Vthreshold2. Spike detectioncircuit 35A is configured to compare the switching voltage Vsw with thefirst and second threshold voltages and provide a decision result. Forexample, the first threshold voltage may be Vin or a percentage of Vin,and the second threshold voltage may be 0V. When the switching voltageVsw is greater than the first threshold voltage, spike detection circuit35A determines that low-side switch 304 is turned off late. Similarly,when the switching voltage Vsw is lower than the the second thresholdvoltage, spike detection circuit 35A determines that low-side switch 304is turned off early. When the switching voltage Vsw is within the rangebetween 0V and Vout, spike detection circuit 35A determines thatlow-side switch 304 is turned off at the exact time. In one embodiment,spike detection circuit 35A may also include a decision result storage360 that stores the decision result whether the turn-off time oflow-side switch is at the exact time, late, or early and provides thestored decision result as an offset control signal 361 to zero-crosscomparator 33A.

FIG. 4 is a circuit diagram illustrating a spike detection circuit 40according to an embodiment of the present invention. Referring to FIG.4, spike detection circuit 40 may include a first differentialoperational amplifier 41 having a first input 411 for receiving theswitching voltage Vsw and a second input 412 for receiving a firstthreshold voltage Vth1, a second differential operational amplifier 42having a third input 421 for receiving the switching voltage Vsw and afourth input 422 for receiving a second threshold voltage Vth2, anddecision making logic 43 for making control decision. For example, thefirst threshold voltage Vth1 may have a voltage level about the voltagelevel of Vin, and the second threshold voltage Vth2 may have a voltagelevel about 0V. In one embodiment, first differential operationalamplifier 41 is configured to operate as a comparator to compare thedifference between Vsw and Vth1 and outputs a comparison result “Late”413 when it determines that Vsw>Vth1. In one embodiment, the seconddifferential operational amplifier 42 is configured to operate as acomparator to compare the difference between Vsw and Vth2 and outputs acomparison result “Early” 423 when it determines that Vsw<Vth2. Decisionmaking logic 43 includes a first input 431 for receiving Late signal 413and a second input 432 for receiving Early signal 423. Decision makinglogic 43 also includes logic gates (e.g., NAND, NOR), latches,flipflops, and the like to make decisions whether the switching voltageVsw includes a glitch (i.e., a positive voltage above Vin or negativevoltage below 0V) at the node 324. In one embodiment, spike detectioncircuit 40 may further include a digital-to-analog circuit forconverting the decision result (i.e., whether low-side switch 304 isturned off at the right time, too early, or too late) to a correspondinganalog offset control signal for controlling the zero-cross comparator33A. It is understood that the spike detection circuit and thezero-cross comparator are only operative when the high-side switch is inthe turn-off state.

Referring back to FIG. 3B, zero-cross comparator 33A includes a firstinput 331 for receiving the switching signal Vsw, a second input 332 forreceiving a reference voltage Vref, and a third input 333 for receivingan offset control signal 361 provided by spike detection circuit 35A.The reference voltage Vref may be a value in the range between 0V andVout. In one embodiment, zero-cross comparator 33A may include adifferential operational amplifier 330 and a variable resistance element315 having a resistance value that can be varied under the control ofthe analog offset control signal 361 receiving at third input 333. Inone embodiment, variable resistance element 315 may include an array ofresistors whose equivalent resistance value is determined by a digitalcontrol word. In some embodiments, a capacitor (not shown) may beconnected in parallel to variable resistance element 315. In an exampleembodiment, variable resistance element 315 may be a MOS transistor, abipolar transistor, a field effect transistor, whose resistance valuecan be adjusted linearly with respect to the control voltage at its gate(base).

FIG. 5A is a graph illustrating the turn-off signal for the low-sideswitch in response to an offset control signal according to anembodiment of the present invention. Referring to FIG. 5A, the slew rateof turn-off signal 343 at output 334 of zero-cross comparator 33A may beadjusted in response to offset control signal 361. For example, line 511represents a slew rate of the output signal at a nominal value ofvariable resistance element 315, which corresponds to the correctturn-off time of low-side switch 304; line 512 represents a slew ratewhen the resistance value of variable resistance element 315 increases;and line 513 represents a slew rate when the resistance value ofvariable resistance element 315 decreases. FIG. 5B is a graphillustrating the adjusted slew rates shown in FIG. 5A being converted toa digital turn-off signal for the low-side switch after the outputsignal with adjusted slew rates passes through an inverter buffer (notshown). For example, the turn-off signal for the low-side switch may bedelayed by an amount Δt1 or advanced by an amount Δt2 in relation to anominal time t by adjusting the resistance value of variable resistanceelement 315. It is understood that the inverter buffer (not shown) canbe implemented in the zero-cross comparator or in the switching voltageregulator.

In another embodiment, zero-cross comparator 331 may include aseries-string of delay elements, e.g., a resistor array whose equivalentresistance value can be determined by a digital code word. In this case,digital-to-analog converter 44 of spike detection circuit 35A shown inFIG. 4 is omitted. Logic circuit 43 will output control signals (i.e.,digital code words) for controlling the series-string of delay elements(i.e., determining the equivalent resistance value of the series-stringof delay elements or resistor array) to adjust the turn-off signaltiming of low-side switch 304. In yet another embodiment, zero-crosscomparator 331 may include an internal offset shift to Vref (332) value.In this case, digital-to-analog converter 44 of spike detection circuit35A shown in FIG. 4 is omitted. Logic circuit 43 will output controlsignals for controlling the value of the offset affecting the comparatoroutput switching with a delay corresponding to the offset value added.This adjusts the turn-off signal timing of low-side switch 304.

FIG. 6 is a simplified flow chart of a method 600 for controlling aturn-off time of a low-side switch in a switching voltage regulatorhaving a high-side switch and the low-side switch connected in seriesbetween an input voltage supply and ground. Method 600 may include:

At 601: providing a spike detection circuit coupled to the switchingvoltage regulator. In one embodiment, the spike detection circuit may bespike detection circuit 35A shown in FIG. 3A or spike detection circuit40 shown in FIG. 4 and described in sections above.

At 603: determining a glitch at an output terminal of the switchingvoltage regulator. The glitch may be a positive glitch caused by a lateturn-off of the low-side switch. The glitch may be a negative switchcaused by an early turn-off of the low-side switch. The glitch may notbe present when the low-side switch is turned at the ideal time.

At 605: varying a slew rate of an output signal of a comparator inresponse to the glitch. After determining that a glitch is present, themethod may also provide a control signal to the comparator to vary theslew rate of the output signal according to the determined glitch. Forexample, the output signal slew rate curve of the comparator can be madesteeper if the glitch is determined to be a positive glitch, i.e., thelow-side switch was turned off late, or the output signal slew ratecurve of the comparator can be made slower than the nominal value if theglitch is determined to be a negative glitch, i.e., the low-side switchwas turned off early.

At 607: buffering the output signal. The output signal is then bufferedto drive the low-side switch. In one embodiment, the buffer may beintegrated in the comparator. In another embodiment, the buffer may beintegrated in the switching voltage regulator. In some embodiments, thebuffer, the comparator, and the switching voltage regulator areintegrated within the same integrated circuit.

At 609: providing the buffered output signal to turn off the low-sideswitch.

As described above, a late or early turn-off of the low-side switchcauses the inductor current Iout to flow across the body diode of thehigh-side switch or the low-side switch, thereby increasing power lossin the switching voltage regulator. Another cause of power loss isassociated with the non-overlap period of the high-side and low-sideswitches. As used herein, a dead time is defined as a time when neitherthe high-side switch nor the low-side switch is turned on. When bothhigh-side and low-side switches are only momentarily on at the sametime, a large shoot-through current will flow between the input supplyvoltage and ground. However, when a dead time is selected to exceed anoptimal time period, the inductor current Iout flows through the bodydiode of the low-side switch and causes voltage ringing at the switchingnode LX. Also, it causes power loss through the body diode. Embodimentsof the present invention provide a circuit and method for reducing powerloss associated with the dead time.

FIG. 7 is a simplified block diagram of a switching voltage regulator 70for minimizing power loss during a dead time according to an embodimentof the present invention. Referring to FIG. 7, switching voltageregulator 70 include a logic circuit 71 for providing driver signalsPdrive and Ndrive, a dead-time control circuit 72, a high-side switch702, a low-side switch 704, and a spike detection circuit 75. Switchingvoltage regulator 70 further includes an inductor L and a capacitor C.The inductor L and the capacitor C may be integrated with switchingvoltage regulator 70 in the same integrated circuit, or the inductor Land the capacitor may be external to switching voltage regulator 70. Inone embodiment, dead-time control circuit 72 may include twocross-coupled gates and a pair of delay elements each of which havingone terminal coupled to an output of one of the two cross-coupled gatesand another terminal coupled to an input of one of the two cross-coupledgates. Spike detection circuit 75 may include a differential operationalamplifier operative to compare the switching voltage Vsw with athreshold voltage and provides a dead-time control signal 752 todead-time control circuit 72.

FIG. 8 is a simplified circuit diagram of a switching voltage regulator80 according an embodiment of the present invention. Referring to FIG.8, dead-time control circuit 82 includes a first gate 801, a second gate802, a first delay element 803, and a second delay element 804. Firstgate 801 has a first input coupled to the Pdrive signal, a second inputcoupled to an output of first delay element 803, and a first outputcoupled to an input of second delay element 804. Second gate 802 has athird input coupled to an output of second delay element 804, a fourthinput coupled to the Ndrive signal, and a second output coupled to aninput of first delay element 803. Switching voltage regulator 80 mayfurther include a first buffer 805 having an input coupled to the firstoutput of first gate 801 and an output coupled to high-side switch 702,and a second buffer 806 having an input coupled to the second output ofsecond gate 802 and an output coupled to low-side switch 704. Spikedetection circuit 85 may include a differential operational amplifierconfigured to compare the switching output voltage Vsw with a thresholdvoltage for determining the presence of a glitch. The threshold voltagemay have a level ranging around 0V. Spike detection circuit 85 may alsoinclude a logic circuitry for providing a dead-time control signal 752to first and second delay elements 803, 804. In one embodiment, spikedetection circuit 85 may be similar to spike detection circuit 35A shownin FIG. 3B. In another embodiment, spike detection circuit 85 may besimilar to spike detection circuit 40 shown in FIG. 4.

In one embodiment, the first and second delay elements may be RC delayelements. FIG. 9 is a schematic circuit diagram of RC delay elements 90according to an embodiment of the present invention. RC delay elements90 may include a variable resistance element 91 and a capacitor C 92.Variable resistance element 91 may an MOS transistor, a field effecttransistor, and the like having a resistance value that can be adjustedunder the control of a voltage applied at its gate. In one embodiment,the voltage applied to variable resistance element 91 is the analogdead-time control signal 752 provided by spike detection circuit 85(e.g., provided by the analog-to-digital converter 44 shown in FIG. 4).In one embodiment, the first and second delay elements may be acurrent-starved delay cell, where the delay is controlled through acurrent supplied to the delay cell. This can vary under the control of avoltage applied to a gate of an MO S transistor.

In one embodiment, first gate may be an OR gate, and second gate may bean AND gate. In another embodiment, first gate may be an AND gate, andsecond gate may be an OR gate. In yet another embodiment, first gate maybe a NOR gate, and second gate may be a NAND gate. In still anotherembodiment, first gate may be a NAND gate, and second gate may be a NORgate. One of skill in the art will appreciate that a NAND gate in thepositive logic system may be expressed by a NOR gate in the negativesystem.

FIG. 10 is a graph illustrating waveforms of driver signals 807 and 808for the respective high-side switch and the low-side switch according toan embodiment of the present invention. As shown in FIG. 10, the deadtime is variable, thereby enabling the control of the turn-on orturn-off time of the high-side switch and the low-side switch. One ofskill in the art will appreciate that the delay elements provide thedelay only when the gate outputs change from a high level to a low levelin the case of an OR gate, alternatively, the delay elements provide thedelay only when the gate outputs change from a low level to a high levelin the case of an AND gate. By having different types of logic gates forthe first and second gates, the dead time can be controlled both in thehigh-to-low and low-to-high transitions.

FIG. 11 is a simplified flow chart of a method 1100 for controlling adead time of a switching voltage regulator according to an embodiment ofthe present invention. Referring to FIG. 11, method 1100 may include:

At 1101: providing a dead-time control circuit between a logic circuitof the switching voltage regulator and the high-side and low-sideswitches.

At 1103: monitoring a switching voltage at an output terminal of theswitching voltage regulator by a spike detection circuit.

At 1105: determining whether the switching voltage exceeds a thresholdvoltage by the spike detection circuit.

If the switching voltage is determined to exceed the threshold voltage,generating, at 1107, a control signal and provide the control signal tothe dead-time control circuit to adjust a dead time between a firstdriver signal and a second driver signal and go back to 1103. If theswitching voltage is determined not to exceed the threshold voltage,maintaining, at 1109, the dead time between the first driver signal andthe second driver signal and go back to 1103.

While the present invention is described herein with reference toillustrative embodiments, this description is not intended to beconstrued in a limiting sense. Rather, the purpose of the illustrativeembodiments is to make the spirit of the present invention be betterunderstood by those skilled in the art. In order not to obscure thescope of the invention, many details of well-known processes andmanufacturing techniques are omitted. Various modifications of theillustrative embodiments, as well as other embodiments, will be apparentto those of skill in the art upon reference to the description. It istherefore intended that the appended claims encompass any suchmodifications.

Furthermore, some of the features of the preferred embodiments of thepresent invention could be used to advantage without the correspondinguse of other features. As such, the foregoing description should beconsidered as merely illustrative of the principles of the invention,and not in limitation thereof. Those of skill in the art will appreciatevariations of the above-described embodiments that fall within the scopeof the invention. As a result, the invention is not limited to thespecific embodiments and illustrations discussed above, but by thefollowing claims and their equivalents.

What is claimed is:
 1. A voltage regulator for supplying an outputvoltage to a load, the voltage regulator comprising: a switching modulecomprising a high-side switch and a low-side switch connected in seriesfor generating the output voltage based on an input voltage; and a spikedetection circuit configured to detect a presence of a glitch on theoutput voltage, and in the event that the glitch is present, determinewhether the glitch is a positive glitch higher than the input voltage ora negative glitch, and adjust a turn-off timing of the low-side switchbased on a determination result.
 2. The voltage regulator of claim 1,wherein the spike detection circuit comprises an operational amplifierhaving a first input terminal for receiving the output voltage, a secondinput terminal for receiving a first threshold voltage, a third inputterminal for receiving a second threshold voltage, the first thresholdvoltage being greater than the input voltage, and the second thresholdvoltage being lower than a ground potential, the operational amplifierbeing configured to output the determination result.
 3. The voltageregulator of claim 2, wherein the spike detection circuit furthercomprises a storage unit configured to store the determination result.4. The voltage regulator of claim 2, further comprising a zero-crossingcomparator having an first input for receiving the output voltage, asecond input for receiving a reference voltage in a range between theoutput voltage and the ground potential, a third input for receiving thedetermination result, and an output for providing a control signal tothe switching module based on the determination result.
 5. The voltageregulator of claim 4, wherein the zero-crossing comparator comprises avariable resistance element having an equivalent resistance configuredto control a timing of the control signal in response to thedetermination result.
 6. The voltage regulator of claim 4, wherein thezero-crossing comparator comprises a resistor array having an equivalentresistance configured to control a timing of the control signal inresponse to the determination result.
 7. The voltage regulator of claim4, wherein the zero-crossing comparator is only operative when thehigh-side switch is in a turn-off state.
 8. The voltage regulator ofclaim 1, wherein the spike detection circuit comprises: a firstdifferential operational amplifier for detecting the positive glitch; asecond differential operational amplifier for detecting the negativeglitch; a logic circuit coupled to the first and second differentialoperational amplifiers and configured to provide an indication signalfor indicating a width of the positive glitch and a width of thenegative glitch.
 9. The voltage regulator of claim 1, wherein the spikedetection circuit is only operative when the high-side switch is in aturn-off state.
 10. The voltage regulator of claim 1, wherein thehigh-side switch is a p-channel transistor, and the low-side switch isan n-channel transistor.
 11. A method for controlling a load-currentzero-crossing of a switching regulator having a high-side switch and alow-side switch, the method comprising: generating, by the switchingregulator, an output voltage based on an input voltage; detecting, by aspike detection circuit, a presence of a glitch on the output voltage ofthe switching regulator; determining, by the spike detection circuit, inthe event that the glitch is present, whether the glitch is a positiveglitch higher than the input voltage or a negative glitch; adjusting aturn-off timing of the low-side switch based on a determination result.12. The method of claim 11, wherein detecting the presence of a glitchcomprises: determining whether the output voltage is greater than afirst threshold voltage or less than a second threshold voltage, thefirst threshold voltage being the input voltage, and the secondthreshold voltage being a ground potential.
 13. The method of claim 12,wherein detecting the presence of a glitch further comprises:determining a width of the glitch.
 14. The method of claim 13, whereinthe width of the glitch indicates whether the turn-off timing of thelow-side switch is early or late with respect to an ideal turn-off time.15. The method of claim 11, wherein adjusting the turn-off timing of thelow-side switch comprising adjusting a resistance value of a variableresistance element of a zero-cross comparator.
 16. The method of claim15, wherein the spike detection circuit and the zero-crossing comparatorare only operative when the high-side switch is in an ideal turn-offstate.
 17. The method of claim 11, further comprising: storing thedetermination result in a decision result storage unit of the spikedetection circuit.
 18. The method of claim 11, wherein the load-currentzero-crossing comprises a crossing of a current flowing across aninductor disposed between a load and the high-side switch and thelow-side switch.
 19. The method of claim 11, wherein the high-sideswitch is a p-channel transistor, and the low-side switch is ann-channel transistor.
 20. The method of claim 19, wherein the positiveglitch is a voltage above the input voltage by an amount equivalent to avoltage drop across a body diode of the p-channel transistor, and thenegative glitch is a voltage below a ground potential by an amountequivalent to a voltage drop across a body diode of the n-channeltransistor.